California Could Be Hit by an 8.2 Mega-Earthquake, and It Would Be Catastrophic

The magnitude 8.2 earthquake that ravaged southern Mexico on Sept. 7 was the largest to shake the country in nearly a century. Like California, Mexico is a seismically active region that has seen smaller quakes that have caused death and destruction. But the Sept. 7 temblor is a reminder that even larger quakes — while rare — do occur. Scientists say it’s possible for Southern California to be hit by a magnitude 8.2 earthquake. Such a quake would be far more destructive to the Los Angeles area because the San Andreas fault runs very close to and underneath densely populated areas.

Collapsed Santa Monica Freeway bridge across La Cienega Boulevard, Los Angeles after the Northridge earthquake, Jan. 17, 1994. Robert A. Eplett/FEMAThe devastating quakes that hit California over the last century were far smaller than the Sept. 7 temblor, which Mexican authorities set at magnitude 8.2 and the U.S. Geological Survey placed at 8.1. Mexico’s earthquake produced four times more energy than the great 1906 San Francisco earthquake, a magnitude 7.8, which killed 3,000 people and sparked a fire that left much of the city in ruins.

Southern California’s most recent mega-quake was in 1857, also estimated to be magnitude 7.8, when the area was sparsely populated. (That was considerably stronger than the 7.1 quake that hit Mexico on Tuesday, causing buildings to collapse and leading to a significant loss of life)... A magnitude 8.2 earthquake would rupture the San Andreas fault from the Salton Sea — close to the Mexican border — all the way to Monterey County. The fault would rupture through counties including Los Angeles, Riverside and San Bernardino...